It is reported in this paper that the results of allolepathy test of Ruppia maritima L. on Chlorella vulgaris with co-culture in reclaimed wastewater and pure culture in the filtrate of liquious cultured the macrophyte.Chlorella vulgaris co-cultivated with Ruppia maritima in reclaimed wastewater indicated that Ruppia maritima had remarkable inhibition on Chlorella vulgaris.On co-culture experiment, at 96h inhibition ratio was 88.86%;the competition of the nutrients had contribution to the growth which inhibited the Chlorella vulgaris.On pure culture experiment with the filtrate of liquious cultured entire plant, leaves and roots of Ruppia maritima, the results of pure culture was inhibition activities on the growth of Chlorella vulgaris with the filtrate of entire plant, leaves and roots of Ruppia maritima, at 96h inhibition ratio of leaves and roots were 48.91%, 34.71% and 14.12%, the al lolepathic effect of equal coefficient Et of plant, leaves and roots were -0.2448, -0.1317 and -0.0901.The allolepathy parameter Et of Ruppia maritime on Chlorella vulgaris was derived from the modified Logistic equation.Leaves and roots of Ruppia maritima were capable of releasing allelopathically active compounds, but the inhibitory activity of allelopathically active compounds mainly came from the leaves tissue.